With the scale down of devices, deposition of dielectric films with good step coverage is desirable. Traditional ALD is a self-limiting process, whereby alternated pulses of reaction precursors saturate a substrate surface and leave no more than one monolayer of material per pulse. The deposition conditions and precursors are selected to ensure self-saturating reactions, such that an adsorbed layer in one pulse leaves a surface termination that is non-reactive with the additional gas phase reactants of the same pulse. A subsequent pulse of different reactants reacts with the previous termination to enable continued deposition. Thus each cycle of alternated pulses leaves no more than about one molecular layer of the desired material. The principles of ALD type processes have been presented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, the disclosure of which is incorporated herein by reference.
As described herein, Atomic Layer Deposition (ALD) processes can be used to deposit multi-component thin films. ALD provides good step coverage on three-dimensional structures. Deposition of multi-component thin films are described, for example, in U.S. Pat. Nos. 7,108,747, 7,713,584, U.S. Patent Application Nos. 20060088660 and 20080072819, the disclosures of which all are incorporated herein by reference.
When depositing a multi-component oxide thin film having components A and B using an ALD process, it is common to require uneven cycles of each component to generate a desired thin film. For example, in order to create an SrTiOx thin film from SrO and TiO2 it may be desirable, or necessary, to generate the thin film using a pulse ratio of 3 SrO precursor pulses to every 2 TiO2 precursor pulses.
According to current ALD manufacturing processes, in order to generate such a thin film requiring the 3:2, SrO to TiO2 ratio, three cycles of SrO would be followed by 2 pulses of TiO2. That set of five pulses is then repeated as many times as necessary to generate a thin film having the desired characteristics. Such manufacturing processes however develop thin films having undesirable thickness or composition uniformity.
As technology advances, and reduces in size, the importance of the uniformity of multi-component oxide thin films increases. Therefore, there exists a need for a process by which to produce desired multi-component oxide thin films utilizing uneven ratios of component precursors in the manufacturing process which produces thin films having superior uniformity.